Adjustable vascular ring, means for treating SFS syndrome and implantable kit comprising such a ring, mould and method for obtaining such a ring

ABSTRACT

The invention relates to a perivascular ring having an inner diameter adjustable by inflation/deflation and adapted to be implanted and closed about a vessel for controlling the inner diameter of said vessel and thus the flow and/or pressure of a fluid flowing in said vessel. The ring of the invention is capable of regulating blood flow to the liver, in particular after an hepatectomy or hepatic transplant, and to substantially improve the survival chances of the patient. The ring according the invention has an adjustable inner diameter (O i ) for implantation and locking about a vessel.

TECHNICAL FIELD

The field of the invention is that of medical devices that can beimplanted by surgical route around a biological duct, in particular avessel and more particularly a blood vessel such as the portal vein, inorder to allow adjustment of the diameter of the duct and therefore ofthe flow rate of a fluid (blood) capable of circulating therein.

These implantable medical devices are more precisely vascular rings thatcan be inflated and deflated using a fluid, so as to adjust their innerdiameter and thus the inner diameter of the ducts/vessels around whichthey are intended to be implanted.

The invention also relates to the manufacture of such vascular rings andconcerns more specifically the moulds and methods for manufacturing thevascular rings involving said moulds.

The invention also relates to the kit that can be implanted by surgicalroute and allow control of the inner diameter of a vessel and, as aresult, the flow rate of a fluid circulating therein.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

It is known to implant medical devices constituted by inflating bandingrings, around blood vessels of patients in order to restrict blood flow,for example on the pulmonary arteries. This is the subject of the patentapplication US2008/0097947A which discloses an annular banding devicefor the pulmonary artery, comprising an inflating banding ring intendedto be put in place around the pulmonary artery of the patient, aninflation tube connecting the banding ring to an insufflating button.The banding ring is generally C-shaped and comprises an external thinrigid silicone layer and an internal thin silicone layer, forming aninflating balloon. The rigid silicone external layer or wall extendsinto the end zone corresponding to the opening of the “C” so as to formlocking means making it possible to adapt the inflation bandage deviceto the diameter of the pulmonary artery. The ring also comprises holesfor the passage of sutures allowing it to be fixed to the pulmonaryartery of the patient. The inflation of this ring leads to thedeformation of the thin flexible silicone inside wall in a centripetaldirection, which causes a compression of the pulmonary artery and areduction in its inner diameter. The inflation is carried out using aliquid which is injected using the insufflating button which can also bepulled to allow deflation of the ring.

This type of inflatable vascular ring exists not only in cardiac surgerybut also in hepatic surgery. Thus the PCT application WO2010/102661Adescribes an implant for controlling the blood flow inside a vessel,namely more precisely the portal vein. This control is particularlycritical for the success of liver transplants and major hepatectomies.In fact, it is vital for the patient that blood flow in the portal veinjust after the transplantation or hepatectomy is not excessive, at therisk of unacceptably damaging the hepatic graft. This phenomenon isknown by the name of “Small For Size (SFS)” syndrome. This syndromeoccurs in the case of a portal flow rate greater than 260 ml/min per 100g of liver and/or a portal pressure greater than 20 mm Hg. It causes alethal alteration of the liver.

The perivascular adjustable implant according to WO2010/102661Acomprises an inflatable balloon (3) of open annular shape, arrangedinside a non-extendible band (4). The inflation balloon is connected toan injection chamber by an inflation tube. The non-extendible outer bandis equipped with locking means (6) of the ring or vessel. The inflationand the deflation of the annular inner balloon makes it possible torestrict (inflation) or increase (deflation) the inner diameter of thevessel around which the implant is placed. This implant comprises, onthe inside of the inflatable balloon, means for measuring the bloodpressure inside the vessel. FIGS. 2A to 2D of WO2010/102661A show thechange in shape of the inflatable balloon as it is inflated. It appearsthat the inner wall of the inflatable balloon changes from a circularshape (FIG. 2A) to a shape leaving a passage by growing, which is causedby a bulge in the inflation balloon. It is clear that such a compressionof the portal vein is equivalent to crushing, causing a stenosis whichleads to turbulences in the blood flow resulting in risks of thrombosis.

This implant according to WO2010/102661A does not therefore allowsatisfactory control of the flow rate and/or of the blood pressureinside the vessels, in particular the portal vein. This implant does notprovide an effective solution to the problem of SFS syndrome, after ahepatectomy or a liver transplant.

OBJECTIVES OF THE INVENTION

In this context, one of the objectives of the present invention is toprovide a sophisticated device for control of the circulation flow rateof a fluid inside a biological duct, in particular of the blood in theportal vein, so as to regulate the flow rate or the blood pressure inthe liver, in particular after a hepatectomy or a liver transplant and,as a result, to significantly improve the patient's chances of survival.

The present invention also aims to provide a perivascular ring with aninner diameter that can be adjusted by inflation/deflation and isintended to be implanted and closed around a vessel in order to controlthe inner diameter of this vessel and thus the flow rate and/or thepressure of a fluid circulating in this vessel, this ring having tosatisfy at least one of the objectives set out below:

-   -   i to have a behaviour and change in shape for adjustment of the        diameter of the vessel, which leads to no crushing of the latter        and therefore no stenosis accompanied by secondary effects that        are harmful to the patient.    -   ii to allow reliable control of the flow rate and/or pressure of        the fluid, in particular of the blood, circulating in the duct        around which it is implanted.    -   iii to be simple to put in place and lock around the biological        duct/vessel the flow rate and/or of the internal pressure of        which is to be controlled.    -   iv to be comfortable and have no harmful effect on the health of        the patient.    -   v to be biocompatible.    -   vi to be secure and reliable, in particular untearable.    -   vii to offer optimum locking around the biological duct, for        example the vessel, the flow rate and/or the pressure of which        is to be controlled.    -   viii to be capable of industrial mass production according to        stringent standards and at the best cost.    -   viii to be radio-opaque at least in part.    -   ix to be easily implantable, in a stable, non-aggressive and        effective manner in terms of control of the flow rate.

The present invention also aims to provide a method and a mould forobtaining the ring which is viable and simple to implement on anindustrial scale.

The present invention also aims to provide a kit that can be implantedby surgical route, for controlling the flow rate and/or pressure insidea vessel, comprising a perivascular ring meeting the above objectives asdefined in the present disclosure, an inflation/deflation module andoptionally a suture for closing the ring, this suture being selected tobreak in the event of overpressure in the ring.

BRIEF DESCRIPTION OF THE INVENTION

These objectives, among others, are achieved by the present inventionwhich relates to a ring with an adjustable inner diameter O_(i),intended to be implanted and closed around a biological duct, preferablya vessel, in order to control the diameter of this duct and thus theflow rate and/or pressure of a fluid circulating in the duct, this ringcomprising:

-   -   an outer belt with a diameter that is substantially constant in        the closed position;    -   an inner chamber that can be inflated and deflated in the closed        position, so as to vary its inner diameter O_(i);    -   a flexible inflation/deflation tube, one end of which is        connected to the inner chamber and the other end of which is        intended to be connected to inflation means;        the outer belt and the inner chamber forming open collars, at        least one of which, preferably that forming the outer belt, is        equipped with means for closing the ring around the duct;        characterized in that the inner chamber, at rest and in the        closed position, has an inner diameter O_(ir) corresponding to        the smallest reduced diameter required when in use, for        controlling the diameter of the duct.

The duct is advantageously a blood vessel, such as for example theportal vein.

The ring according to the invention is a remarkable development of theknown implantable perivascular rings intended for controlling the bloodflow rate, in particular the portal flow rate and/or pressure.

Due to its original structure, this ring proposes a novel type ofnon-traumatic pneumatic or hydraulic modulation of the flow rate orpressure of the fluid, for example the blood, circulating in the duct,for example a vessel.

This constitutes significant progress towards successful hepatectomiesand liver transplants, by offering the practitioner an effective meansof combating SFS syndrome.

This ring is moreover secure, reliable, of a reasonable cost and capableof being produced on an industrial scale in compliance with the requiredquality and productivity standards.

The invention also relates to a mould and a method for obtaining thisring, as well as a kit that can be implanted by surgical route, forcontrolling the flow rate or blood pressure, comprising this ring and aninflation/deflation module intended to be connected to the proximal endof the inflation/deflation tube, in order to allow the in situ injectionof an inflation/deflation fluid into the inner chamber or the in situextraction of an inflation/deflation fluid out of the inner chamber.

Definitions

In the present disclosure, each singular and each plural interchangeablyrefers to a plural or a singular.

The definitions which are given below by way of examples, are intendedto facilitate the interpretation of the present disclosure.

“duct” and “vessel” interchangeably refer to a channel in which abiological fluid circulates, for example blood or lymph.

“closed position” of the ring means that the two ends of the ring arefixed to each other, so that the ring defines a cylinder.

The “at rest” state of the ring means that the pressures inside andoutside the inner chamber of the ring are balanced at the ambientatmospheric pressure. When the ring is positioned and closed around theduct, at rest, it is at least partially inflated so that it restrictsthe diameter of the duct, compresses it and reduces it.

The distal end of the flexible tube is its free end situated outside thebody of the patient in whom the implant is put in place, i.e. the freeend intended to be connected to the inflation/deflation means.

The proximal end of the flexible tube is the end opposite to its distalend, i.e. the end connected to the ring according to the invention.

By hardness D1, D2, is meant the Shore A hardness of the material(s)constituting the ring.

By the smallest reduced diameter required when in use for controllingthe diameter of the duct is meant the inner diameter of the innerchamber at rest, i.e. partially inflated, for which the diameter of theduct Dc, on which the ring is intended to be positioned, is restrictedand reduced to a minimal value Dcr with respect to the normal diameterDcn (or maximum diameter) that the duct would have in a “normal state”without this ring around it. For each duct to be enclosed, the Dcr valuethat the duct must reach once the ring is positioned around it isdetermined. For example, if the duct is the portal vein, the smallestreduced diameter required when in use for controlling the diameter ofthe portal vein is the inner diameter O_(ir) of the inner chamber withwhich the diameter of the portal vein is restricted by 55%, preferably50% with respect to the natural, normal diameter Dcn of the portal veinwith no restriction. It must obviously be borne in mind that thediameter Dc of the duct can also be reduced if necessary, once the ringis positioned around it, by inflation of the inner chamber of the ringor increased by deflation of the inner chamber. By “normal state”, ismeant the state of the duct with no restriction and in which thebiological fluid circulates at a non-pathological, normal, averagebiological flow rate. In the normal state, the biological duct has anormal diameter Dcn, which depends on the biological species, sex andage of the individual.

Preferred Features and Advantages of the Invention

The fact that the inner chamber, at rest and in the closed position, hasan inner diameter O_(ir) corresponding to the smallest reduced diameterrequired when in use for controlling the diameter of the duct, makes itpossible to define a shape of the inner chamber, with no invagination,bulge or fold, in which the ring reduces, to a certain level, thediameter of the duct, and therefore the flow rate and/or pressure of thefluid circulating in the duct.

The smallest reduced diameter required for use can be defined by thelevel of reduction (e.g. expressed as a percentage of reduction) of thediameter of the duct around which the ring is intended to be implantedand locked. According to the invention, this percentage of reductioncorresponds to the requirements for use. In particular, as regards themodulation of the flow rate and/or blood pressure, such as in the portalvein, it is provided, according to a remarkable feature of theinvention, that the ring has a O_(ir) selected in order to reduce by atthe most 55%, preferably by at the most 50%, the diameter of the vesselaround which the ring is intended to be arranged and locked. Thus, whenthe ring according to the invention is positioned and closed around theportal vein, at rest and therefore already partially inflated, the ringrestricts the diameter of the vein. It reduces this diameter by at themost 55%, preferably 50%. Depending on the requirement and desiredtreatment of the patient, it is then possible either to further inflatethe ring and thus further reduce the diameter of the inner chamber andas a result the diameter of the vein, or to deflate the ring andincrease the diameter of the inner chamber and as a consequence thediameter of the vein around which it is positioned.

The percentage reduction is adapted depending on the ducts around whichthe ring is intended to be put in place and also depending on the aim ofthe operation and of the positioning of such a ring. Thus, in the caseof SFS, it is desirable to reduce the diameter of the portal vein by 55%or even 50%. As a general rule, a human portal vein has a diameter of 15mm (±5 mm). The ring positioned and closed around the portal vein, in arest position, i.e. inflated (but not to its maximum) must reduce thediameter to 6.75 mm (±2.25 mm) for a 55% reduction of the diameter ofthe portal vein.

When the vessel is a vein (flexible wall), the diameter of the vessel isthat for which the flow rate of the circulating fluid corresponds to thenormal average biological flow rate.

In practice, during a hepatectomy or a liver transplant, the surgeonputs the open ring according to the invention in place around the portalvein, upstream of the liver, and closes this ring by firmly fixing itsends to each other. The portal vein is thus restricted so that itsdiameter is reduced by at the most 55%, preferably by at the most 50%.The portal diameter considered is, for example, that corresponding tothe normal average portal flow rate in humans, namely 700 ml (+/−200 ml)per minute, i.e. approximately 50 ml/min per 100 g of liver, in ahealthy individual; or also approximately 260 ml/min per 100 g of liver,in a patient having undergone a major hepatectomy (80% of the liverremoved). This flow rate value of approximately 260 ml/min per 100 g ofliver corresponds to the maximal value, below which the patient isexposed to SFS syndrome.

The practitioner can choose, as a function of the clinical data at theirdisposal, to further reduce or to increase the portal diameter byinflation or deflation of the inner chamber, in order to fix the portalflow rate at a value that is desirable for the patient, by graduallybringing this value back to normal, whilst taking the patient's state ofhealth into account.

This procedure could be applied to other medical or non-medical species,for which the positioning of a perivascular ring is prescribed in orderto reduce and then optionally increase the intravascular flow rate.

The diameter of the biological duct may be reduced using the ringaccording to the invention, until the duct is obstructed (clamping ofthe duct).

According to a preferred embodiment of the invention, the ring is ameans intended to be put in place and locked around the portal vein of apatient, upstream of the liver, in order to reduce, by at the most 55%,preferably by at the most 50%, the diameter D_(vp) of the portal vein,down to a minimal value D_(vpr) and in order to then allow themodulation of D_(vp) between D_(vpr) and its normal diameter D_(vpn) (ormaximum diameter) in which the ring does not reduce D_(vp), saidmodulation consisting of deflating the ring in order to increase O_(i)and therefore D_(vp), from to D_(vpr) to D_(vpr), so as to reduce theportal pressure downstream of the ring and maintain the intrahepaticpressure at a value less than or equal to 20 mm Hg, preferably at 15mmHg and thus treat/limit SFS (Small For Size) syndrome, suitable forhepatectomies and liver transplants.

The invention therefore relates, in particular, to a means for treatingSmall For Size syndrome suitable for hepatectomies and livertransplants, characterized in that it comprises the ring as defined inthe present disclosure.

The invention also relates to a method for the treatment of Small ForSize syndrome suitable for hepatectomies and liver transplantscharacterized in that it essentially consists of:

-   -   putting in place and locking around the portal vein of a        patient, upstream of the liver, a perivascular ring as defined        in the present disclosure, in order to reduce by at the most        55%, preferably by at the most 50%, the diameter D_(vp) of the        portal vein down to a minimal value D_(vpr);    -   modulating D_(vp) between D_(vpr) and its normal diameter        D_(vpn) (or maximum diameter) in which the ring does not reduce        D_(vp); said modulation consisting of deflating the ring in        order to increase O_(i); and therefore D_(vp) from D_(vpr) to        D_(vpn), so as to reduce the portal pressure downstream of the        ring and maintain the intrahepatic pressure at a value less than        or equal to 20 mm Hg, preferably at 15 mmHg;    -   gradually bringing D_(vp) back to its value D_(vp) over a        sufficient period of time so that the intra-hepatic pressure        stabilizes at a value less than or equal to 20 mm Hg, preferably        at 15 mmHg;    -   then unlocking the ring and removing it.

According to a preferred feature of the invention, the inner chamber hasno invagination at rest and in the closed position of the ring, and theinner edge of the inner chamber that is intended to be in contact withthe duct has a substantially circular, flat shape, with no invagination,fold or bulge. It conforms to the outer wall of the duct on which it ispositioned whilst restricting the diameter of the duct.

Preferably, O_(i) decreases by inflation and increases by deflation.

The fact that the inner chamber of the ring is inflated at rest in theclosed position around the duct and, moreover, that its inner diameterO_(i) decreases by inflation and increases by deflation, makes itpossible to safely and reliably control the flow rate and/or theinternal pressure of a fluid circulating in the biological duct/vesselaround which the ring is put in place in the closed position, limitingthe associated risks of stenosis and thrombosis.

According to a notable feature of the invention, the ring ischaracterized in that the inner chamber forms no invagination (norfold), nor bulge and has a “substantially” circular inner shape, in theclosed position of the ring, when this inner chamber is inflated. By“substantially” circular is meant, within the meaning of the presentdisclosure, a closed plane curve, the points of which are at the samedistance from the centre with a tolerance of plus or minus 20%,preferably 10%, of O_(i).

As indicated above, the ring according to the invention is an opencollar which can be defined by at least one of the following features:

-   -   (i) the inner chamber forms, at rest and in the non-closed        position of the ring, an open collar on an angular sector less        than or equal to, in ° and in increasing order of preference, 5;        4; 3; 2; 1;    -   (ii) the outer belt Ruins, at rest and in the non-closed        position of the ring, an open collar over an angular sector less        than or equal to, in ° and in increasing order of preference,        10; 8; 6; 4; 2.

In the preferred embodiment, the open collar has no angular sector but anarrow channel, the ends to be joined in order to close the ring beingparallel when the ring is in open position at rest.

In one possible version of the invention, the flexible inflation tubecomprises at least one non-return valve.

According to an interesting feature of the invention aimed at improvingthe reliability of the locking of the ring around the biologicalduct/vessel, the ring is characterized in that the outer belt isequipped with closing means comprising two outer lips extending in thecentrifugal direction and capable of being joined to one another in adiametral plane, in reversible manner, in order to close the ring aroundthe duct, preferably using (a) suture(s), preferably resorbable,threaded through at least one perforation made in these outer lips.

In order to allow it to be visible to X-rays, it may be useful,according to the invention, for the ring to comprise at least oneradio-opaque part, for example a radio-opaque insert.

The ring according to the invention can be also characterized bymanufacturing features. Thus, this ring can advantageously be obtainedby moulding using a mould. The latter has features which make itpossible to indirectly define the ring according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description of a preferred embodiment of the ringaccording to the invention, will highlight other remarkable features.

This detailed description is given with reference to the attachedfigures in which:

FIGS. 1A & 1B represent perspective views of the ring according to theinvention, deflated and in the closed and open positions respectively.

FIGS. 2A, 2B & 2C represent top views of the ring according to theinvention, at rest and respectively in closed (2A) and open positionsaccording to a preferred embodiment (FIG. 2C) and according to anembodiment variant (FIG. 2C), ready to be positioned around the duct.

FIG. 3 is a longitudinal cross-sectional view along the cutting plane ofFIG. 2A, 2B or 2C.

FIGS. 4A & 4B are front views of the ring shown in FIGS. 2A & 2B or 2Crespectively.

FIG. 4C is a longitudinal cross-sectional view along the cutting planeIV-IV of FIG. 3.

As shown in the attached figures the ring (1) according to the inventionis a ring that can be inflated and deflated so as to vary its innerdiameter (O_(i)) so as to be able to compress and release the segment ofbiological duct for example of blood vessel such as the portal vein,around which said ring (1) is intended to be implanted and closed forcontrolling the flow circulating in the duct/vessel (2) represented bydot-and-dash lines in the figures.

The ring (1) comprises:

-   -   an outer belt (3);    -   an inner chamber (4) that can be inflated and deflated;    -   a flexible inflation/deflation tube (5).

The outer belt (3) has a substantially constant inner diameter and outerdiameter. This outer belt (3) is similar to an open collar (FIGS. 1B,2B, 2C & 4B) the 2 free ends of which have closing means (7) comprisingtwo outer lips (3 ₁, 3 ₂) extending in the centrifugal direction andhaving faces (3 ₃, 3 ₄) opposite one another in the open collar (FIGS.1B, 2B, 2C & 4B) and in contact with one another in the closed collar(FIGS. 1A, 2A & 4A). As shown in FIGS. 2A, 2B, 2C and 3. These lips (3₁, 3 ₂) each comprise at least one, in the case in point one,perforation (3 ₅), allowing the passage of at least one suture (notshown in the drawings) preferably resorbable, in order to ensure theclosing (FIGS. 1A, 2A & 4A) of the ring (1) after implantation aroundthe vessel (2) the flow rate of which is to be regulated. This suturecompletes the closing means (7). Advantageously, this suture is selectedin order to break in the event of overpressure of the inner chamber (4)of the ring (1). This arrangement is a safety feature for preventing astenosis of the duct, which could have irreversible consequences for thepatient. This arrangement also allows the surgeon to open the ring (1)by over-inflation, before proceeding to remove this ring (1).

This outer belt (3) is made of a semi-rigid material of hardness D1 andselected from the group of biocompatible elastomers, comprising or, evenbetter, constituted by silicone elastomers or analogues.

The inner chamber (4) is an inflatable and deflatable balloon having, atrest and in the closed position (FIG. 2A), a diameter (O_(ir)), whichcorresponds to the minimum diameter value (+/−10%) desired for use,namely a diameter which restricts the diameter Dc of the duct aroundwhich it is positioned as soon as it is put in place. In the case of thehuman portal vein, the normal diameter or maximum value D_(vpn) beforereduction is, for example, comprised between 10 mm and 20 mm. The ringput in place and locked around the portal vein has an inner diameterO_(ir) which determines a reduction of the portal flow rate preferablyby at the most 50%.

Under the effect of the inflation, the inner chamber (4) increases involume in a centripetal direction, which reduces its inner diameterO_(i). The deflation produces a reduction in the volume of the innerchamber (4), in centrifugal direction, in order to compress or releaserespectively the vessel (2) of a patient (e.g. portal vein), aroundwhich the ring (1) is put in place and closed using the means (7).

In the preferred embodiment shown in FIG. 2B, the open collarconstituted by the outer belt (3) has an opening extending along anarrow channel delimited by the parallel faces 3 ₃ and 3 ₄ of the outerlips 3 ₁ & 3 ₂.

In the embodiment variant shown in FIG. 2C, the open collar constitutedby the outer belt (3) has an opening extending over an angular sector α₃equal to approximately 10° in this example. In this variant, the innerchamber (4) is an open collar the ends of which delimit an openingextending over an angular sector α₄ equal to approximately 5°.

As shown by the figures, in particular FIG. 3, this inner chamber (4) isannular and comprises, in the example shown in the drawings (FIG. 3), anouter wall (4 ₁) in contact with and/or firmly fixed to the outer belt(3) and a curved inner wall (4 ₂), the outer wall (4 ₁) and the innerwall (4 ₂) being connected to one another by lateral faces that aresubstantially straight in the example selected, but which could becurved and are denoted by the reference numbers (4 ₃, 4 ₄). The innerchamber (4) could be toroid-shaped according to a variant.

The inner wall (4 ₂) forms the inner edge of this inner chamber (4).This inner edge (4 ₂) has a circular shape, when the ring is at rest(neither inflated: no internal overpressure, nor deflated: no internallow pressure) in the closed position (FIGS. 1A, 2A & 4A), and notarranged around a duct. According to the invention, this circular shapeof the inner edge (4 ₂), and, more generally, of the inner chamber (4)is maintained once the ring is arranged around a duct (e.g. vein) andduring the inflation and deflation operations. This means that the innerchamber (4) forms no invagination, fold or bulge, either in the reststate, in the inflated state, or in the deflated state. The shape of theinner edge (4 ₂) and, more generally, of the inner chamber (4), remains“substantially” flat and circular, once the ring is arranged around aduct (e.g. vein), from the inflated rest state to a further inflatedstate and a deflated state corresponding to the requirements of use. Inthe case of adjustment of the human portal flow rate, these inflated anddeflated states are included, for example, within the following innerdiameter O_(i) limits (in mm and in increasing order of preference):[5-25]; [6-24]; [7-20].

As shown in FIGS. 2A, 2B, 2C, 3, 4C, a radio-opaque band (4′) isinserted between the inner chamber (4) and the outer belt (3), in theouter wall (4 ₂).

The inner chamber (4) is, for example, made of a flexible material ofhardness D2 and selected from the group of biocompatible flexibleelastomers comprising or, even better, constituted by siliconeelastomers or analogues.

According to a preferred feature of the invention, the hardness D1 ofthe outer belt (3) is greater than the hardness D2 of the inner chamber(4). For example, D1 is comprised between 60 and 100, preferably 70-90,for example of the order of 80 Shore A.

According to another preferred feature of the invention, the hardness D2of the inner belt (4) is comprised between 5 and 40, preferably 10 and30, and even more preferably of the order of 20 Shore A.

The flexible inflation/deflation tube (5) is connected by its proximalend (5 p) to the inside of the inner chamber (4) and by its distal end(5 d) to inflation means not shown in FIG. 3. The inflation/deflationtube (5) is diametrically opposite the opening of the ring (1) as can beseen in FIGS. 1A, 1B, 2A, 2B, 2C, 3 and 4C. The outer belt (3) has anend piece (6) which extends towards the outside and which receives theproximal end (5 p) of the inflation tube (5). This inflation tube (5)can be equipped with a plastic non-return valve.

The inflation tube (5) can be made of the same material as the innerchamber (4), for example, with a hardness D3 comprised between D1 andD2, e.g. of the order of 60 Shore A.

The inflation/deflation means (not shown in the drawings) areconstituted for example by a syringe, preferably a screw syringe makingit possible to make precise inflation/deflation adjustments byinjection/tapping of the inflation/deflation fluid. The ring (1)according to the invention can be put in place around the vessel (2) bythe standard surgical route (laparotomy) or by the coelioscopic route.The closing of the ring (1) is carried out by suture with resorbablesutures, though the perforation (3 ₅) of the inner chamber (3)—closingmeans (7)—. The ring (1) thus positioned has a reduced inner diameter(O_(ir))) which restricts the vessel (2) to the smallest reduceddiameter required for use (Dvpr) and thus limits the flow rate orpressure, for example blood, to a given level dependent on O_(ir). Thepractitioner then proceeds to adjust the flow rate and/or pressure, byinflation/deflation. In the case of hepatectomy or liver transplant,this adjustment aims to maintain an intrahepatic pressure less than orequal to 20 mm Hg, preferably 15 mm Hg. O_(i) is gradually increased bydeflation. D_(vp) and with it the flow rate and/or the blood pressure inthe portal vein therefore also increase(s) gradually, until D_(vp)reaches D_(vpn) (normal diameter or maximum diameter of the portalvein). The time taken for this rise of D_(vpr) to D_(vpn) is that whichis necessary for hepatic parenchyma in order to recover a capacity tocontain the intrahepatic pressure below 20 mm Hg, preferably below 15 mmHg, for the pressure and/or the flow rate downstream of the ring,corresponding to a portal diameter equal to D_(vpn).

This significantly limits the risks of SFS syndrome for the patient.

The ring according to the invention, once closed by a suture or sutures,preferably bioresorbable, can be reopened by over-inflation of the innerchamber, which causes the suture or sutures to break. After opening thering (1), the practitioner can also take advantage of the over-inflationof the ring (1), in order to keep the free ends of the ring (1) apartfrom each other and thus facilitate its extraction. This has theadvantage of avoiding further anaesthesia and its associated risks.

The invention claimed is:
 1. A ring for treating Small For Size syndromesuitable for hepatectomies and liver transplants, the ring having anadjustable inner diameter and being intended to be implanted and closedaround the portal vein, upstream of the liver, in order to control thediameter of the portal vein and thus the flow rate and/or pressure of afluid circulating in the portal vein, the ring comprising: an outer beltcomprising two outer lips extending in the centrifugal direction andcapable of being joined to one another in a diametral plane, in areversible manner, in order to put the ring in a closed position aroundthe portal vein, the outer belt having a constant diameter in the closedposition; an inner chamber that can be inflated and deflated in theclosed position, so as to vary an inner diameter of said inner chamber;a flexible inflation/deflation tube, a proximal end of which isconnected to the inner chamber and a distal end of which is intended tobe connected to inflation means; inflation means connected to the distalend of the flexible tube; and at least one suture to join the outer lipsto one another to close the ring, the suture being selected to break inthe event of overpressure in the ring, the outer belt and the innerchamber forming open collars, at least one of which is equipped withmeans for closing the ring around the portal vein; wherein the innerchamber, at rest and in the closed position, has an inner diametercorresponding to a smallest reduced diameter required when in use forcontrolling the diameter of the portal vein, the inner diameter of theinner chamber being configured to reduce by at the most 55% the diameterof the portal vein D_(vp) to a minimal value D_(vpr), the inflationmeans being controlled to allow the modulation of the diameter of theportal vein D_(vp) between the minimal value D_(vpr) and a normaldiameter D_(vpn) in which the ring does not reduce the diameter of theportal vein D_(vp), said modulation consisting in deflating the ring inorder to increase the inner diameter, so as to reduce the portalpressure downstream of the ring and maintain the intrahepatic pressureat a value less than or equal to 20 mm Hg.
 2. The ring according toclaim 1, wherein the inner chamber has no invagination at rest and inthe closed position of the ring and in that the inner edge of the innerchamber intended to be in contact with the portal vein has asubstantially circular shape.
 3. The ring according to claim 1, whereinthe inner diameter of the inner chamber decreases by inflation andincreases by deflation.
 4. The ring according to claim 1, wherein thereopening of the ring, after it is implanted and closed around theportal vein, is achieved by over-inflation of the inner chamber.
 5. Thering according to claim 1, wherein said suture is threaded through atleast one perforation made in said outer lips.
 6. The ring according toclaim 5, wherein the suture is resorbable.
 7. The ring according toclaim 1, comprising at least one radio-opaque part.
 8. A kit that can beimplanted by surgical route, allowing the adjustment of the innerdiameter of a duct and thus the flow rate of a fluid circulating in thisduct, this kit comprising: a ring according to claim 1; aninflation/deflation module intended to be connected to the distal end ofthe flexible inflation/deflation tube, in order to allow the in situinjection of an inflation/deflation fluid into the inner chamber or thein situ extraction of an inflation/deflation fluid out of the innerchamber.
 9. The ring according to claim 1, wherein the inner diameter isadapted to reduce by at the most 50% the diameter of the portal veinD_(vp) to the minimal value D_(vpr).
 10. The ring according to claim 1,wherein the inflation means are controlled to reduce the portal pressuredownstream of the ring and maintain the intrahepatic pressure at 15 mmHg.